Chances are, he is eating, and you just aren't seeing him do so. Food needs to nearly fall on a bichir's nose before he can find it, and sometimes even then, it won't take it. He's probably cruising the substrate after lights out and eating what he finds.
If you're truly worried though, try some small pieces of raw, cut shrimp or krill, delivered directly to him with a long pair of tweezers. My bichirs love shrimp and krill, and the days I feed it are the only times I see them actively feed.
Otherwise, just keep an eye on him and watch for the obvious signs of starvation.